A clear dividing line between important work and busywork. Before there was email, there were letters. It amazed (and humbled) me to see the amount of time each person allocated simply to answering letters. Many would divide the day into real work (such as composing or painting in the morning) and busywork (answering letters in the afternoon). Others would turn to the busywork when the real work wasn’t going well. But if the amount of correspondence was similar to today’s, these historical geniuses did have one advantage: the post would arrive at regular intervals, not constantly as email does.

The Daily Routines of Geniuses by Sarah Green in Harvard Business Review.